docs: def img_opacity(image, opacity):
      """
      Reduce the opacity of a PNG image.
  
      Inspiration: http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/362879
  
      :param image: PNG image file
      :param opacity: float representing opacity percentage
      :return: Path to modified PNG
      """
      # Validate parameters
      assert 0 <= opacity <= 1, 'Opacity must be a float between 0 and 1'
      assert os.path.isfile(image), 'Image is not a file'
  
      # Open image in RGBA mode if not already in RGBA
      im = Image.open(image)
      if im.mode != 'RGBA':
          im = im.convert('RGBA')
      else:
          im = im.copy()
  
      # Adjust opacity
      alpha = im.split()[3]
      alpha = ImageEnhance.Brightness(alpha).enhance(opacity)
      im.putalpha(alpha)
  
      # Save modified image file
      dst = _add_suffix(image, str(str(int(opacity * 100)) + '%'), ext='.png')
      im.save(dst)
      return dst